| Fluoride is an essential trace element which was found in the atmosphere, water, soil. coal. food, dental and industrial uses. Because of its great reactivity, fluoride is the anion F". which can be bonded to another element to form organic fluoride and inorganic fluoride.Fluoride is the most important caries-preventive agent in dentistry. Sodium fluoride (NaF) is one of the most common in soluble fluoride salts. Therefore, it is easy to release fluoride ions. Although right amount of fluoride is beneficial to plants and animals and even humans, excessive intake of fluoride will produce toxic effects.With the development of industry, a mass of fluoride was produced by human activities, such as metallurgy, production of brick, ceramics and glasses, and processing of nuclear fuel and manure, which cause the increase of the fluoride concentration in the air and water. Therefore, organisms become easier to be exposed to the fluoride. In this paper, we have studied the chronic fluoride exposure on the Big toad Bufo gargarizans and the effect of fluoride on the development of the larvae at different concentrations. The effect of fluoride on the development of anura larvae were investigated using morphological measurement, histological and molecular method. The main results as follows:1. After exposed to different concentration of NaF at different development stages (G28. G33, G38). the metamorphic data, such as body weight (BW). total length (TOL) were evaluated in order to reveal the effect of fluoride on the larval development. The results showed that differences in sensitivity between the developmental stages occurred at the beginning of the exposure time (G28). And also, with the exposure time prolongation. NaF increased the body weight of tadpoles at the lower concentrations (≤10.00mg/L). However, high concentration of NaF decreased the body weight (50.00mg/L). In addition, the total length of tadpoles seemed to be unaffected by-exposure NaF.2. The double-stained method with alcian blue and alizarin red were used to investigate the skeletal development of the larvae exposed to different concentrations of NaF at different development stage. The results showed that the double-stained skeleton of larval at stage G33and G38exposed to50.00mg/L NaF found no difference compared to the control group. In addition, from the perspective of morphology. 50.00mg/L NaF did not cause an effect on the cranium skeleton. However, with the development of tadpoles.50.00mg/L NaF-treated group change the development process of the bone and delay the calcification of bone. It indicated that the inhibitory effect of50.00mg/L NaF was gradually enhanced with the prolongation of exposure time. In contrast, low concentrations of NaF (≤10.00mg/L) can promote the development of bone. It determined the significant difference by observing the color of bone specimens.3. After fluoride exposure at sublethal concentration at different development stages (G28, G33, G38, G42), gross morphological of thyroid glands from tadpoles were examined in the present study, the results showed that tadpoles exposed to1.00mg/L,5.00mg/L,10.00mg/L NaF showed a marked increase in glandular size. In contrast, the size of thyroid gland treated with50.00mg/L NaF tadpoles declined except at stage G33. It may indicate that stage G33is a critical period of thyroid development. Perhaps the phenomenon is a compensatory response. It still needs further research.4. Hematoxylin-esosin stained paraffin sections of thyroid gland were used to evaluate the histological appearance of thyroid glands collected from larvae at different stages in control and50.00mg/L NaF-treated groups. The results showed that there was little change in the thyroid gland at stage G28. Some collapsed follicles containing little or no colloid were observed in glands from50.00mg/L NaF treated tadpoles at stage G33in the present study. With the prolongation of exposure time, when the tadpoles developed into the stage G38and G42, the arrangement of follicular epithelial cells became looser. And also, the distance of follicular became wider. It showed apparent degradation phenomenon, which indicated high concentrations of NaF produced obvious toxic effects to thyroid gland, and then block the development of toads.5. D2and D3gene expression in whole tissues were examined by semiquantitative RT-PCR analysis. The results showed that the expression of D2and D3gene were no obvious difference between control group and NaF-treated groups. |
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